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Equine protozoal myeloencephalitis (
Equine Protozoal Myeloencephalitis: Introduction) is a common disease of horses that produces a nonsuppurative, often necrotizing, meningoencephalomyelitis. Horses are an aberrant host for the causative organism, usually
Sarcocystis
neurona
, but less commonly, other protozoa cause the disease. Any age horse can be affected. Neurologic signs are extremely variable and often asymmetric, reflecting involvement anywhere in the CNS. Ataxia and paresis are common. Other potential signs include obscure lameness, focal muscle atrophy, and cranial nerve dysfunction. Diagnosis is based on neurologic signs, exclusion of other potential causes, detection of antibodies to
S
neurona
in the CSF, and response to treatment. Treatment protocols include ponazuril (5 mg/kg/day, PO for 28 days) or pyrimethamine (1 mg/kg/day, PO) and sulfadiazine (20 mg/kg/day, PO) for 90-180 days. Many horses recover with treatment, but permanent neurologic deficits are possible. Prevention is difficult but involves reducing access of opossums (the definitive host) to horses, feed, and water. A vaccine is also available. |
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Neosporosis (
Neosporosis: Introduction) is caused by
Neospora
caninum
, a protozoan that can cause a nonsuppurative encephalomyelitis, most commonly in dogs. The life cycle of this organism has not been defined. Many previously reported cases of toxoplasmosis in dogs were probably neosporosis. Infection in young puppies typically causes ascending paralysis with rigid contraction of the muscles of one or both pelvic limbs. Other organs, including muscle, liver, and lungs, can be affected. Diagnosis is based on serology or identification of the
organism in tissue samples. Early treatment with clindamycin or sulfadiazine and pyrimethamine may be effective, but the prognosis is poor. |
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Toxoplasmosis (
Toxoplasmosis: Introduction) is caused by
Toxoplasma
gondii
and can occasionally cause a nonsuppurative encephalomyelitis in dogs and cats. Infected cats often have evidence of disease in other organs, such as uveitis, pancreatitis, and respiratory disease. Dogs with toxoplasmosis often also have other diseases, such as canine distemper. Diagnosis is based on identifying the organism in tissue or a 4-fold increase in IgG antibody in paired sera. In cats, a high concentration of IgM antibody in serum or CSF is supportive.
Clindamycin or sulfadiazine and pyrimethamine are recommended for treatment. |
